The problems with this chain of logic is that no one has the amount of information necessary to prove a correlation, much less a causal chain between border policy and starvation and therefore policy should NOT be made in response to mere unproven hypothesis;

the hypothesis is weak since population growth is negatively, not positively, affected by displacing millions of one's own population, the conclusion should be the opposite;

further it has a crucial weakness in that you're not just shifting around people (with the power to provide no less), but also economic strength (which in turn is involved in food production);

it puts on a scale life that is in need of saving *right now* against life that may be in need of saving in the future;

it neglects non-african and african countries which can easily support a bigger population;

is kind of missing the point altogether: the waste of human life in just the top 5 refugee countries alone far outshadows the (recorded) casualties at sea and our primarily goal should be to reduce the most casualties.

NOT to ensure these casualties happen by way of starvation and dehydration and then still achieve the same thing you're citing as a problem: "more food to go around".